Throughout the world there is increasing interest in converting renewable biomass to usable products such as ethanol. Conversion of wood to ethanol has been practiced during wartime due to a shortage of liquid fuels. Reported in Ind. and Eng. Chem. Vol. 38 No. 9, P. 890 (1946). Because of poor yields and consumption of chemicals the conversion was found not to be economical for peacetime use. Present day interest in hydrolysis of biomass is to provide an alternative fuel source to avoid dependence on unreliable imported petroleum crude oil for liquid fuels. Biomass often contains hemicellulose and lignins accompanying the cellulose contained in the biomass. Hydrolysis of biomass is employed to produce glucose and pentoses. Biomass is a term used to describe material containing cellulose including: paper, pulp, wood waste, sawdust, municipal solid waste (MSW), agricultural wastes, fabrics, and cotton.
A state of the art hydrolysis process, described in U.S. Pat. No. 6,007,636, uses a concentrated acidic liquor to liquefy the carbohydrates in the biomass. A solvent is then employed to form a precipitate of the liquefied carbohydrates in the biomass. The resulting solids are then filtered to separate the solids from the solution of the concentrated acidic liquor and solvent. The resulting filtrate containing concentrated acidic liquor and solvent is then subjected to a separation of the solvent and recycle of the acidic liquor and recovery of solvent is achieved.
Also, a state of the art process being developed by workers at the University of Arkansas, is described in U.S. Pat. No. 4,608,245 and in FY 1997 BIOCHEMICAL conversion/ALCOHOL FUELS PROGRAM: Annual Report page A-85. It employs high concentration of sulfuric acid to convert corn stover to sugars. They describe a process scheme to separate sugars contained in the concentrated sulfuric acid using a heavy boiling solvent to dissolve the sulfuric acid and a low boiling solvent to dissolve the heavy boiling solvent. They also report that this method has a loss of solvents and a loss of sulfuric acid which is neutralized with lime.
Reported in the above named report, on page A-15, is a plan by TVA to develop a high concentration of sulfuric acid process. The current focus of TVA is to develop an inexpensive process for recovering the high concentration of sulfuric acid. Thus the problem of recovering sulfuric acid has not yet been solved.
Recovery of the sulfuric acid is reported as an unsolved problem. Thus it is believed that no satisfactory recovery method has yet been developed.
The present concern is about recovering concentrated sulfuric acid from a solution containing ethanol. This invention relates to a method of recycling concentrated sulfuric acid used to produce depolymerized cellulose and hemicellulose contained in a biomass.
Therefore an object of this invention is to obviate many of the limitations and disadvantages of the prior art to separate solvents from a solution containing sulfuric acid.
Another object of this invention is to avoid use of high boiling solvents to recover sulfuric acid.
Still another object of this invention is to remove ethanol from a solution containing sulfuric acid and ethanol.
Yet another object of this invention is to separate concentrated sulfuric acid from ethanol to produce concentrated sulfuric acid for recycling to produce depolymerized cellulose and hemicellulose contained in a biomass.
In addition, another object of this invention is to separate ethanol from a gas humidified by ethanol.
A further object of this invention is to provide recycling of a gas used to remove ethanol from a solution containing sulfuric acid and ethanol.
Additionally, another object of this invention is to utilize low temperature waste energy to maintain a substantially constant thermal equilibrium condition within the vessel to compensate for the energy of ethanol evaporation.
With the above and other objects in view, this invention relates to the novel features and alternatives and combinations presently described in the brief description of the invention.
The present invention, in its broadest aspect, will remove ethanol from a solution containing sulfuric acid and ethanol. By providing a vessel in which ethanol is humidified, and supplying a solution containing ethanol and sulfuric acid, and supplying a gas to humidify the ethanol, the necessary components of the method are hence furnished. The method proceeds by adding the solution to the vessel and combining the gas to form a gas humidified with ethanol, and parting the gas humidified with ethanol from the vessel, and supplying heat to the solution to replace heat of vaporization of the humidified ethanol. The ethanol humidified gas will consequently remove the ethanol from the vessel. The ethanol humidified gas is then separated from the gas to provide ethanol and a gas for recycle to the vessel for use to additionally humidify ethanol. Concentrated sulfuric acid, substantially free of ethanol, is removed from the vessel. In this invention separated concentrated sulfuric acid, from ethanol, is subject to recycle for employment in liquefying cellulose, located in a biomass, followed by hydrolyzing liquefied cellulose in place to form depolymerized cellulose in sulfuric acid. One objective of this invention is to utilize low temperature waste energy to maintain a substantially constant thermal equilibrium condition within the vessel to compensate for the energy of ethanol evaporation.
A method to separate ethanol from a gas is by cooling the humidified gas to substantially condense the ethanol as a liquid and to furnish a gas for recycle.
An alternate method to separate ethanol from a gas is by pressurizing the humidified gas to form a condensation of the ethanol as a liquid and to supply a gas for recycle.